In electronic circuits such as voice operated control (VOX) and automatic gain control (AGC) circuits which are used in two-way radios, the release time section of the VOX or AGC circuit controls how fast the voltage on the output capacitor of the VOX or AGC circuit falls as a function of time. As the release time becomes shorter, the output voltage of the circuit falls quickly, yielding a fast increase in gain. This quick fall in voltage (e.g., increase in gain) causes a phenomenon known as noise pulsing. Noise pulsing occurs when for example the gain in an AGC circuit ramps up very quickly between words or phrases and the background noise becomes amplified. The end result is that during a break in words, a rushing sound similar to the sound a waterfall makes occurs.
The opposite end of the spectrum is when the release time in the AGC circuit is set for a longer period of time (e.g., 5 second region). When a word having a very sharp consonant sound (e.g., words beginning with b, p or t) is spoken into the radio microphone, the sharp consonant sound causes the gain of the AGC circuit to decrease too much and then ramp up very slowly. When this occurs, the first part of the word is lost when the word is transmitted by the radio. For example, if a word like "pirate" were spoken, the radio microphone would react to this rush of air (caused by the "p" sound) as a very loud tone and produce a large output voltage. The AGC circuit in turn reacts to the large output voltage very quickly and tries to reduce the magnitude to a predetermined level. This causes the next portion of the spoken word to be reduced, or even eliminated, by the AGC circuit action previously mentioned. The end result, if the AGC circuit were enabled with a long release time, would be that a word like "pirate" would sound like "p . . . te" at the receiving radio. VOX circuits face similar problems to those mentioned above, given that the peak detector capacitor of the circuit is affected by similar release time problems.
Prior art circuits having release time sections have a major drawback in that most of the prior art circuits require manual change of circuit components in order to adjust the release time of the circuit. Also, prior art circuits tend to be temperature sensitive due to variations in the components such as the discharge resistor, etc. Other drawbacks of prior art circuits include not being able to provide for long release times (e.g., in the order of 5 seconds) due to the exponential discharge characteristics of RC circuits. Another problem with prior art circuits that use a diode as the forward charging switch is that the inherent resistance of the diode causes attack times to be longer. A need thus exists for a circuit which can solve the above mentioned problems and can also have an externally adjustable release time without the need to change external circuit components.